Cylinder device

Abstract

A cylinder device is characterized in: that it selectively realizes an operation-force dependent pressurizing state where brake fluid is pressurized by operation force and a high-pressure-source-pressure dependent pressurizing state where brake fluid is pressurized depending on a pressure from a high-pressure-source device; that there are defined an inter-piston chamber in front of an input piston by an insertion of the input piston into a pressurizing piston, an input chamber in the back of a flange of the pressurizing piston at the pressure from the high pressure source device, and an opposing chamber in front of the flange; and that the cylinder device has a mechanism elastically pressurizing an reaction force chamber formed by a communication between the inter-piston and the opposing chambers, and a mechanism switching communication/not-communication state between the reaction chamber and a reservoir.

The invention claimed is: 
     
       1. A cylinder device which supplies, in order to operate a brake device provided at a wheel, a pressurized brake fluid to the brake device, comprising:
 a housing whose front end portion is closed and which is shaped like a tube; 
 a pressurizing piston which has a main body portion, a flange portion formed on a circumference of the main body portion, and a blind hole opening at a rear end of the pressurizing piston and which is disposed in the housing so as to define (A) a pressurizing chamber which is located in a front side of the pressurizing piston and which pressurizes the brake fluid supplied to the brake device, (B) an input chamber in which a pressure from a high pressure source is inputted in a rear side of the flange portion, and (C) an opposing chamber which is located in a front side of the flange portion with the flange portion interposed between the input chamber and the opposing chamber and which is opposed to the input chamber, respectively; 
 an input piston which is inserted in the blind hole of the pressurizing piston so as to define an inter-piston chamber in front of the input piston by the input piston and the pressurizing piston, and which is connected to an operation member at a rear end of the input piston; 
 an inter-chamber communication passage which always permits communication between the opposing chamber and the inter-piston chamber such that the opposing chamber and the inter-piston chamber serve as a single operation-reaction-force chamber, for accommodating a volume change of the opposing chamber and a volume change of the inter-piston chamber with each other that are caused by a forward and rearward movement of the pressurizing piston; 
 an elastic-force dependent pressurizing mechanism which pressurizes the operation-reaction-force chamber formed by the inter-chamber communication passage depending on elastic force; and 
 a communication-state switching mechanism which selectively realizes a communication state in which the reservoir and the operation-reaction-force chamber communicate with each other and a not-communication state in which they do not communicate with each other, and 
 wherein the cylinder device is configured such that, 
 in the not-communication state, an operation reaction force, in accordance with an operation amount of the operation member, is generated depending on the pressurization of the operation-reaction-force chamber by the elastic-force dependent pressurizing mechanism, while the brake fluid in the pressurizing chamber is permitted to be pressurized in accordance with the pressure inputted from the high pressure source to the input chamber; 
 in the communication state, a volume of the operation-reaction-force chamber is permitted to be reduced, thereby permitting the input piston to come into abutting contact with the pressurizing piston by a forward movement of the input piston, whereby the brake fluid in the pressurizing chamber is permitted to be pressurized by the operation force applied to the operation member. 
 
     
     
       2. The cylinder device according to  claim 1 ,
 wherein the cylinder device includes: 
 a first auxiliary piston which is disposed in the bottom of the blind hole and which defines the inter-piston chamber together with the input piston; 
 a first spring which elastically supports the first auxiliary piston; 
 a second auxiliary piston which is disposed between an outer face of the main body portion of the pressurizing piston and an inner face of the housing and which defines a front side of the opposing chamber; and 
 a second spring which elastically supports the second auxiliary piston, and 
 wherein the cylinder device is configured such that the elastic-force dependent pressurizing mechanism includes the first auxiliary piston, the first spring, the second auxiliary piston and the second spring, and such that, in the communication state, the input piston comes into abutting contact with the pressurizing piston via the first auxiliary piston. 
 
     
     
       3. The cylinder device according to  claim 2 ,
 wherein the elastic-force dependent pressurizing mechanism is configured such that one of a pressurizing force of the first spring and a pressurizing force of the second spring does not increase, when the input piston is moved forward in the not-communication state and an amount of the forward movement thereof goes beyond a predetermined amount. 
 
     
     
       4. The cylinder device according to  claim 1 ,
 wherein the cylinder device includes, in the bottom of the blind hole of the pressurizing piston, (a) an auxiliary piston which defines the inter-piston chamber together with the input piston and (b) a spring which elastically supports the auxiliary piston, and 
 wherein the cylinder device is configured such that the elastic-force dependent pressurizing mechanism includes the auxiliary piston and the spring, and such that, in the communication state, the input piston comes into abutting contact with the pressurizing piston via the auxiliary piston. 
 
     
     
       5. The cylinder device according to  claim 1 ,
 wherein the cylinder device includes: 
 an auxiliary piston which is disposed between an outer face of the main body portion of the pressurizing piston and an inner face of the housing and which defines a front side of the opposing chamber; and 
 a spring which elastically supports the auxiliary piston, and 
 wherein the cylinder device is configured such that the elastic-force dependent pressurizing mechanism includes the auxiliary piston and the spring. 
 
     
     
       6. The cylinder device according to  claim 1 ,
 wherein the input piston includes a main body member which has a shape like a tube, a front end member which closes a front end portion of the main body member such that an internal chamber is defined inside of the main body member and which is allowed to project from and retract into the main body member, and a spring which is disposed in the internal chamber and which biases the front end member in a direction in which the front end member projects, 
 wherein the elastic-force dependent pressurizing mechanism includes the spring, and 
 wherein the cylinder device is configured such that, in the communication state, the front end portion of the main body member of the input piston comes into abutting contact with the pressurizing piston. 
 
     
     
       7. The cylinder device according to  claim 6 ,
 wherein the input piston includes: 
 two springs each of which functions as the spring, one end portion of one of which is supported by one of the main body member and the front end member, and one end portion of the other of which is supported by the other of the main body member and the front end member, which are disposed in a line, and spring constants of which are different from each other; and 
 a floating sheet which is floatingly supported by the two springs so as to be sandwiched between the other end portion of the one of the two springs and the other end portion of the other of the two springs, and which connects the two springs so as to apply elastic forces of the two springs on the front end member, and 
 wherein the elastic-force dependent pressurizing mechanism includes: 
 the two spring and the floating seat; and 
 the cylinder device is configured such that a displacement of the floating seat relative to one of the main body member and the front end member is prohibited so as not to increase an amount of elastic deformation of one of the two springs, where, in a process of retraction of the front end member relative to the main body member, an amount of the retraction exceeds a predetermined amount. 
 
     
     
       8. The cylinder device according to  claim 1 ,
 wherein the communication-state switching mechanism includes a passage for the communication between the operation-reaction-force chamber and the reservoir, and an open/close valve which is provided in the passage and which opens or closes the passage. 
 
     
     
       9. The cylinder device according to  claim 1 ,
 wherein the communication-state switching mechanism includes a passage for the communication between the operation-reaction-force chamber and the reservoir, and a relief valve which opens only when a pressure of the operation-reaction-force chamber exceeds a predetermined pressure.